PORTLAND, Ore. (KOIN) — Pieces of tar washing up on beaches along the Oregon Coast have prompted investigation from state and federal agencies, including the Oregon Department of Environmental Quality.

Officials say they first became aware of “tar patties the size of a sand dollar” when some were found by Cannon Beach visitors on Wednesday. The following day, the Oregon Department of Fish and Wildlife reported finding more patties on near Lincoln City.

These sightings come after multiple birds covered in black oil were found washed up on the coast between Long Beach, Wash. and Lincoln City and tar balls reportedly washed ashore in Southern Washington.

They add the U.S. Coast Guard and other agencies are working to determine the source of the tar-like product, but it is unknown at this time.